Artificial nail structures are a part of a beauty regimen used by many women to impart a well groomed appearance. Artificial nail structures are generally worn on the fingernails of women and provide the appearance of longer nails than the otherwise natural nails. Artificial nail structures are also used to cover broken or weak nails.
The prior art reveals two classes of artificial nail structures. The first class of artificial nail structures are those structures applied as a viscous paste to a detachable and reusable or disposable form attached to the fingernail. These artificial nails are thicker in appearance than a natural nail and can be easily detected. The second class of artificial nail structures are pre-formed extensions that are attached to the nail with a glue and reinforced with a resin, typically with a cyanoacrylate ester resin. The pre-formed nail provides an artificial nail with considerably less thickness than acrylics and gives the nail a more natural look.
As described above, cyanoacrylate ester resins can be used alone to reinforce artificial nail structures. Though these cyanocrylate ester resin coatings are stronger than nail polish they are weaker than sculpted acrylics. Hence, the resins are generally reinforced to give the nails a healthy glow as well as strength to stand up to routine abuse encountered by the artificial nail structures during a normal day. Thus, these resins are typically reinforced with a fiberglass or fabric matrix. The pre-formed matrix is commonly referred to as a nailwrap or an overlay. The nailwrap typically extends over the natural nail and the artificial nail structure.
As described above, nailwraps are used to reinforce artificial nail structures. Nailwraps may also be used alone to reinforce and beautify natural nails.
The following protocols are normally used for applying a nailwrap to the fingernail. The protocols describe using a nailwrap to reinforce an artificial nail structure.
(i) If the nailwrap is self adhesive, the nailwrap structure is placed on the nail and cyanoacrylate ester monomer is spread on it to build the nail. A catalyst or accelerator dissolved in a volatile solvent is then sprayed or brushed or spread on top of this coating. The catalyst is essential in order to accelerate the curing (increase polymerization rate) of the monomer to form a resin. This monomer/catalyst procedure is then repeated. PA1 (ii) If the nailwrap is not self adhesive, a thin layer of cyanoacrylate ester monomer is spread on the nail and the wrap is placed on it when the resin is in a tacky form. This is followed by the monomer/catalyst procedure described in protocol (i) and is repeated twice to build the nail.
In both protocols outlined above, the polymerization of the cyanoacrylate ester starts on the surface and proceeds into the bulk of the monomer, i.e., into the cyanoacrylate ester monomer and toward the surface of the fingernail. The main drawback with this procedure is that several growing polymer chains are terminated by atmospheric oxygen. This leaves some uncured monomer or oligomer in the "bulk" or at the interface between the artificial nailwrap structure and the fingernail. This uncured monomer/oligomer, having failed to achieve a high molecular weight necessary to impart adhesive properties, hinders the formation of bonds between the adherend (the cyanoacrylate ester resin) and the substrate (the natural fingernail). This leads to several points of high stress (defects) at the interface of the adherend and the substrate. Another reason for these defects is that polymerization begins at the surface and works inward. The monomer rushes to meet the growing polymer, and, as is the case with any polymerization, a degree of contraction occurs as the polymer is formed. This may result in the formation of minute air spaces between the cyanoacrylate resin and the nail. Through routine abuse of the artificial nail structures, the strain energy increases at stressed joints which leads to the gradual appearance of defects as the bond strength weakens between the adherend and the substrate. Rapidly, there comes a point when the strain energy is great enough and releases enough mechanical energy that it exceeds the force of the bonds holding the adherend and the substrate, and the artificial nail structure is chipped or lifted from the natural nail.
Various methods have been designed to attempt to remedy or alleviate this chipping and lifting problem. U.S. Pat. No. 3,425,426, issued to Welanetz (1969) discusses a nail repair provided by a patch material impregnated with a binding solution, i.e., cellulose nitrate, that is a solvent activatable to adhere the nail patch to the nail. The patent of Welanetz provides a cure after the malady has occurred and it does not attempt to prevent the occurrence of the aforementioned drawback.
U.S. Pat. No. 4,299, 243 issued to Umstattd (1981) seeks to remedy the chipping and lifting problem limitation by impregnating the reinforcing material with a quick-drying adhesive.
U.S. Pat. No. 4,450,848 (1984), issued to Ferrigno does not use a reinforcing material but instead uses a clear powder containing acrylic ester polymers and benzoyl peroxide. This solution fails to address the problems caused by initiating the polymerization on the top surface of the artificial nail structure.
U.S. Pat. No. 4,646,765 issued to Lilling (1987) discusses the use of graphite fibers in the cyanoacrylate resin. This procedure yields a final structure that still contains uncured monomers/oligomers at the interface between the adherend and the substrate.
U.S. Pat. No. 4,860,774 issued to Talerico (1989) suggests impregnating the nailwrap with a suspension of resin polymer and monomer. The impregnated wrap is then coated with pressure sensitive adhesive followed by the application of fast drying cyanoacrylate adhesive. The curing process is initiated by moisture in the atmosphere. The patent of Talerico does not provide any remedy that would promote the curing of monomers in the interface of the artificial nail and the natural nail.
U.S. Pat. Nos. 5,219,645 and 5,319,011 issued to Schoon (1994) discuss impregnating the fabric matrix with a cyanoacrylate monomer. This monomer is then cured by a cationic polymerization using a liquid containing organotin compounds. This would be very difficult because electron withdrawing groups, i.e., the cyano and ester groups on cyanoacrylate ester, make the formation of a stable carbocation on the terminal methylene of the acrylate moiety virtually impossible. It is well known that unless the conditions are conducive to the formation of a stable carbocation, it is very difficult to carry out cationic polymerization. The polymerizations of the type mentioned in Schoon can therefore only be carried out with great difficulty using extreme reaction conditions like very high pressure in an explosion proof vessel. Hence Schoon does not provide a solution to the existing dilemma, i.e., of chipping and lifting of the artificial nail structure from the natural nail.
As noted, all the prior art procedures have failed to provide a solution to reduce or eliminate the defects on the interface of the nail (i.e., between the artificial nail structure and the natural nail). There exists a need for a better methodology to promote polymerization and cure the cyanoacrylate ester monomers on the interface.